Chris J Dixon wrote:
Having just extended a flower bed to incorporate what has been
lawn for 40 years, I am left with some pretty solid clay soil.

Gypsum is recommended as a soil improver, but appears to be sold
in garden centres as a proprietary product costing nearly £5 for
2.5 kg.

Hmm. I know it is, but I am scptical.

Our clay overlies enough chalk, and though it helps, it does make the
soil excessively alkaline.

We have found copius additions of orgamic material - peats, topsoils and
manures - and sand, to be a better bet.

Its back breaking work as well. Hire a rotovator or small digger to
break it up and mix it in.





http://www.capitalgardens.co.uk/clay...er-p-6321.html

On the other hand, I can pick up a 25 kg bag of multi-finish
plaster for under £5, and AFAIK this is essentially the same
material.

Any reasons not to go with plaster?


As previous poster says, none really, except it sets hard and can make a
mess of drainage in a particular area. The same is probably true of pure
gypsum.

I've got areas of lawn that I simply left cement and plaster tailings
under and heaps of builders sand, They don't fare well.

The easy way of of making flower gardens in clay, is mulch. That will
decompose into decent topsoil, and you can pull annual weeds out of it.
Wood or coca shell. Or peaty compost.

Or if its for vegetables, cheat: We made raised beds and filled them
with gravel sand and topsoil. After breaking up the underlying clay pan
just a little.



Chris